1. Field of the Invention
The present invention generally relates to implantable prosthetic devices, and more specifically relates to composite prosthetic devices having layers with improved bond strength.
2. Description of the Related Art
It is generally known to use multilayered or composite fabrics in connection with medical procedures. For example, composite fabrics may be used as all purpose pads, wound dressings, surgical meshes, hernia repair meshes, adhesion prevention meshes, tissue reinforcement meshes, defect closure devices, and hemostats.
When treating hernias, one conventional, widely-used surgical procedure involves transferring the hernia content back into the abdomen, and then using sutures to close the abdominal wall opening. When using the above-described conventional procedure, however, a hernial relapse occurs about 20% of the time.
Due to the high relapse rate following conventional hernia operations, many hernia procedures now use artificial implants for reconstructing the abdominal wall. These artificial implants generally include an open mesh material, such as polypropylene or polyester. After implantation, the ideal prosthetic device is incorporated by the surrounding tissue to form a firm connection between the implant and the abdominal wall, does not promote adhesions, has pliability, and provides appropriate strength.
In many instances, artificial implants used for reinforcing the abdominal wall and covering abdominal wall defects are made of multiple layers of a non-absorbable, porous material and an absorbable anti-adhesion material. One multi-layered prosthetic device having a polypropylene mesh, such as that sold under the trademark Marlex®, and an absorbable film, such as that sold under the trademark Gelfilm®, is described by Jenkins et al., in “A Comparison of Prosthetic Materials Used to Repair Abdominal Wall Defects”, Surgery, Vol. 94, No. 2, August 1983, pp. 392-398.
There have been other efforts directed to providing composite or multi-layered prosthetic devices that are efficiently absorbed into a body. For example, commonly assigned U.S. Patent Application Publication No. US 2005/0113849 to Popadiuk et al., the disclosure of which is hereby incorporated by reference herein, discloses a prosthetic repair device including a non-absorbable material, a first absorbable material having a first absorption rate, and a second absorbable material having a faster absorption rate than the first absorption rate. Another embodiment is directed to a prosthetic repair device having a non-absorbable, porous material that is encapsulated with a first absorbable component, and a second absorbable material having a faster absorption rate than the first absorbable component. The prosthetic repair devices described in the '849 publication are designed to exhibit strength and pliability, while efficiently incorporating surrounding tissue at an impressive rate.
U.S. Pat. No. 5,593,441 to Lichtenstein discloses a composite prosthesis and methods for limiting the incidence of postoperative adhesions. The composite includes a mesh fabric and a barrier that prevents exposure of the mesh fabric to areas of potential adhesion. The interstices of the mesh fabric are infiltrated by tissue which secures the prosthesis in place. The composite is positioned with the barrier relative to the region where adhesions may occur, such as the abdominal viscera.
Commonly assigned U.S. Pat. No. 5,686,090 to Schilder et al., the disclosure of which is hereby incorporated by reference herein, teaches a multilayered prosthetic device. The layers of the device are bonded together using materials having different melting points. During manufacture, the implant is heated to a temperature which is higher than the melting point of the material with the lower melting point, but below the melting point of the material with the higher melting point so that one of the layers melts and combines with the adjoining layer. In one embodiment, a film made from a material having a lower melting point is placed between two layers having different melting points. The structure is heated so that the film melts and becomes porous and the two layers are bonded to each other.
Commonly assigned U.S. Patent Application Publication No. US 2005/0010306 to Priewe et al., the disclosure of which is hereby incorporated by reference herein, discloses an Areal implant having a stable, mesh-like base structure having pores of a size in the range from 1.5 mm to 8 mm. The implant includes a synthetic, resorbable polymer film on each of two opposing surfaces. The two polymer films are glued or welded together in pores of the basic structure.
In many instances, the layers of a composite prosthetic device are connected or bonded together using an adhesive. The layers may be bonded together by heating the adhesive to a temperature higher than the melting point of the adhesive. The melted adhesive then flows into the adjacent layers for bonding the layers together. If the heat applied to the device is insufficient to completely melt the adhesive disposed therein, then weak bonding of the layers may result. This problem is particularly likely to occur when laminating multiple layers of absorbable films with mesh structures having poor heat transfer properties.
In spite of the above advances, there remains a need for improved composite prosthetic devices having strength and pliability, and that minimize the likelihood of adhesions forming between the device and the surrounding tissue. Moreover, there remains a need for prosthetic devices having improved bond strength between the layers so that the layers do not pull apart or delaminate. There also remains a need for methods for effectively conducting heat through composite prosthetic devices for effectively melting the adhesive to properly fuse or bond the layers together.